Fabrication processes of semiconductor devices, typified by LSI (Large Scale Integrated circuits) and MOS (Metal Oxide Semiconductor) transistors, include an etching process for removing an insulating film, which is a silicon-containing film such as a silicon oxide film (SiO2), formed over a silicon substrate. The etching process is a process, for example, for partially removing the insulating film over the silicon substrate to obtain a desired pattern. In some cases, an aluminum (Al) film or an alloy film of aluminum and other kinds of metal, which will serve as a wiring layer, is formed over a target substrate, and the etching process is performed on the substrate with both the metal film and silicon oxide film exposed.
One of the etching techniques for removing the insulating film is wet etching in which a silicon substrate to be treated is immersed in an etching solution for a predetermined period of time. A typical etching solution required for wet etching contains hydrofluoric acid, ammonium fluoride and water. However, this type of etching solution lacks an adequate property to prevent corrosion of metal films, such as aluminum film and aluminum alloy film. More specifically speaking, the etching solution strips off a large part of the metal film, or the aluminum film, in a short time at an early stage of the etching process.
Techniques concerning the wet etching of insulating films are disclosed in Japanese Unexamined Patent Application Publication Nos. S49(1974)-84372 (PTL1) and S59(1984)-184532 (PTL2), Japanese Patent No. 4397899 (PTL3), Japanese Unexamined Patent Application Publication No. S52(1977)-108351 (PTL4) and Japanese Patent No. 3292108 (PTL5). PTL1 to PTL3 introduce a mixed solution of hydrofluoric acid, ammonium fluoride and acetic acid for etching. According to PTL4 and PTL5, etching processes are performed with a mixed solution of hydrofluoric acid, ammonium fluoride and polyalcohol.